As is well known, a linear motor comprises a stator portion and a mover portion. Normally, the stator portion is configured by disposing a plurality of permanent magnets (hereinafter referred to as magnets) or electric magnets (hereinafter referred to as electromagnets) side by side in a moving direction. On the other hand, the mover portion comprises a coil and is configured so as to be movably combined with the magnets with a gap defined therebetween. It is necessary that the coil be supplied with electric power corresponding to the weight of the mover portion and the weight of a load mounted on the mover portion and it is necessary to supply the electric power to the moving coil through wiring. Therefore, appropriate measures are required for the wiring between the mover portion and the stator portion. If a battery is installed on the mover portion for power feeding to the coil, it is possible to eliminate the wiring between the mover portion and the stator portion. In this case, however, long-term traveling is not possible.
Further, the linear motor comprising the coil as the mover portion has a problem of heat generation in the coil. That is, various measures are required for cooling the generated heat of the moving coil.
For solving the foregoing problems, there is also proposed a moving magnet type linear motor using a magnet as a mover portion. The linear motor of this type comprises a stator portion having a plurality of coils arranged side by side in series in a moving direction. The mover portion has one or more magnets and is configured so as to be movably combined with the coils with a gap defined therebetween (see, e.g. Japanese Unexamined Patent Application Publication (JP-A) No. H6-54516).
On the other hand, the linear motor requires a position detecting device for stopping the mover portion at a predetermined position. In the hitherto linear motor, a linear scale is disposed on the stator portion along the moving direction and a magnetic sensor is provided on the mover portion so as to face the linear scale, thereby detecting the position of the mover portion. That is, the position of the mover portion is detected by the position detecting device in the combination of the linear scale and the magnetic sensor. By controlling the current to the coils based on detected values of the position detecting device, running control and position control of the mover portion are executed.
However, the linear scale is not low-priced and there are problems caused by the linear scale, such as an increase in cost of parts, an increase in cost of operation for installing the linear scale, and an increase in cost of maintenance.
It is therefore an object of this invention to provide a moving magnet type linear motor that enables running control without a linear scale.
It is another object of this invention to provide a moving magnet type linear motor that enables position control without a linear scale.